US2119132A - Recovery of tar acids - Google Patents

Description

May 3l, 1938. J. 3` HATMAN '2,119,132v

RECOVERY OF TAR ACIDS Filed April 15, 1935 Patented May 31, 1938 UNITED STATES ArsN'r OFFICE RECOVERY or TAR ACIDS Application April 13, 1935, Serial No. 16,240'

8 Claims.

This invention relates tothe art of recovering tar acids from tar and particularly to a process by which the tar acids may be separated in a simple, economical manner from the tar produced incidental to the manufacture of coke. An arrangement of apparatus that it has been found advantageous to use in the performance of the new process is also a part of this invention.

In accordance with the usual process of manufacturing coke, a. quantity of tarry material results as a by-product. This tarry material, or crude tar as it will hereafter be called, has a specic gravity of around 1.06 to 1.18 and ordinarily contains from 21/2 to 6% of tar acids and up to about 10% of water. The tar acids, which consist mainly of phenol and its homologues, such as the cresols and xylenols, are valuable commercially but are quite dilicult to isolate according to known procedures.

The practice heretofore has usually been to dehydrate the crude tar either by evaporating off the water or centrifuging. After dehydrating, the crude tar is distilled in a tar still and separated into two fractions, the fraction boiling below 270 C. being known as tar oil and the remainder simply as tar, or as tar residue. The tar acids are substantially wholly contained in the tar oil and are present thereinin a concentration of between and 25%.

This tar oil fraction is subjected to further treatment to separate these acids. Such treatment ordinarily consists in intermixing the tar oil with an aqueous caustic soda solution of a concentration suilcient to convert the tar acids into phenolates, cresolates and the like. These compounds, which will hereafter be referred to generally as phenolates, dissolve readily in the caustic solution and are subsequently separated from the tar oil by allowing the mixture to settle into an aqueous layer and an oil layer and then decanting. The aqueous solution so obtained is thereafter treated by blowing carbon dioxide gas through it, or may be treated with an acid, usually sulphuric, to convert the dissolved compounds back into tar acids. The tar acids, being insoluble, are thereafter separated from the resulting solution of sodium carbonate or sodium sulphate by gravity settling.

The difficulty with such a process is that it requires a dehydration and. distillation of the heavy tarry material which is difcult and troublesome and which many coke plants are not equipped to accomplish. Hence the tar must often be sold without extracting the tar acids therefrom, to refineries especially equipped for this work and these refineries must be equipped to carry out the relatively long and involved process outlined above.

The present process has been conceived to overcome difficulties involved in the practice of the process now in use and to produce relatively pure tar acids simply and expeditiously, directly from the original tarry material as it is produced by the coke plant. According to an application Serial No. 754,718, filed by Charles M. 10 Ambler, Jr. and-Charles E. Underwood on November 26, 1934 which has matured into Patent #2,081,692, it has been found that if this original tarry material is mixed directly with a basic solution such as an aqueous solution of caustic 15 soda or caustic potash, capable of converting the tar acids into the corresponding phenolates, and thereafter separated from such solution with sufcient promptness to avoid emulsion difficulties, such separation can be effected and the separated solution will contain substantially all of the tar acids in the form of soluble phenolates. These compounds may thereafter be reconverted into tar acids by the addition of acid, and separated.

The present invention is an improvement upon the process and apparatus described in the Ambler et al. application and provides a modified process according to which the aqueous solution of phenolates formed by the action of water and caustic soda upon the tar, is recycled until the concentration of phenolates therein isv greatly increased and-'the eii'ciency with which these phenolates may be separated from the aqueous solution is materially bettered. Furthermore, the g5 present invention provides a system of apparatus by which this novel process may be performed either continuously or by the batch. Further details that add to the efciency or desirability of the new process and apparatus will appear more A fully from a consideration of the following detailed description of the preferred mode of practicing the invention and of the system of apparatus which has been found especially adapted for the performance of this process.

In the drawing, forming a part of this application, the new process and system of apparatus for performing it are illustrated in their preferred form by a flow sheet. According to this ilow sheet the original raw materials are water, tar, caustic soda solution and stack gas from the coke ovens. In place of at least part of the water, after the process has been started in operation, a solution of phenolates from previously extracted tar is supplied.

According to illustrated process, a caustic soda solution, usually of a concentration of about 8% by weight is supplied to the mixer through a constant head pump and a proportioningfmeter in approximately the ratio of one gallon of caustic solution to each iive or six gallons of tar, the tar also being fed through a constant head pump and the proportioning meter. At the same time an aqueous liquid, either Water or phenolate solution from a previous extraction or a mixture of the two, is fed through another` constant head pump and the proportioning meter into the mixer. The aqueous liquid may either enter the mixer with the caustic solution and the tar or may be supplied to theseconstituents after they have been partially mixed, in accordance with the process described in the above mentioned application. The ratio of the aqueous liquid to the tar is usually about 2 to l by volume but may be as low as 1 to 1. The ratio of caustic solution to tar is preferably adjusted so that approximately 1.4 pounds of caustic soda are added for every gallon of tar acids in the tar.

After the mixing has been completed, preferably in the manner described by the above mentioned application, although it may be done in any other manner found convenient, the mixture is brought to a temperature of around 80 C. and centrifuged to separate the tar from the aqueous solution of phenolates formed by the reaction of the caustic soda solution upon the tar acids in the tar.

The resulting aqueous solution of phenolates is passed into a storage tank from which it may be returned by a pump and be recycled through the same process. As this recycling is continued the supply of water to the system may be d iminished or stopped altogether, with the result that the concentration of phenolates in the solution increases until a concentration is reached at which the phenolate solution contains a sufficient percentage of phenolates to enable their recovery to be efliciently made. At that time the whole of the phenolate solution may be directed into other apparatus for recovering the tar acids therefrom, or a portion of the phenolates may be directed into such apparatus and the remainder recycled to collect more tar acids. The concentration of phenolates in the solution will not increase indefinitely, for the caustic soda solution added tends to dilute the phenolate solution and thus to reduce the concentration and in addition a certain amount of water is extracted from the tar itself. Usually there is around six to ten percent of water in the tar as it is originally received and of this all but about 0.5 to 1.5 percent is extracted and passes into the phenolate solution.

As the phenolate solution is recycled, the addition of caustic soda solution may be discontinued, if desired, and sufficient caustic soda, in solid form, added to the phenolate solution to maintain the desired concentration. Alternatively the addition of the caustic soda solution may be continued and the rate of addition adjusted to maintain the proper concentration, namely, around 1.4 pounds ofcaustic soda per gallon of tar.- Y

If an amount of phenolate solution equal to the amount of caustic added plus the amount of water extracted from the tar, is removed to the recovery apparatus continuously and no additional water is added, the system willreach an equilibrium point at which the concentration of the phenolates in the phenolate solution Will be substantially constant. A point of equilibrium will also be reached if water is added at a delinite rate with the recycled phenolate solution and a suflicient quantity of the phenolate solution is Withdrawn continuously to balance this water, as well as the water taken from the tar and the caustic solution.

The phenolate solution taken from the above described section of the system passes through a pump and suitable heating apparatus which raises its temperature to around 90 C. to a springing tower where it passes countercurrent to gas from coke oven stacks. In so doing the phenolate solution absorbs carbon dioxide and the tar acids are re-formed. Some of the water and a portion of the tar acids are Volatilized and pass off through the top of the tower, but these are condensed in a suitable condenser and passed to a settling tank together with the portion of the tar acids and water solution that remains liquid. In the settling tank the re-formed tar acids separate from the aqueous solution of carbonates formed in the springing tower. The carbonate solution is passed to suitable apparatus where it is regenerated into caustic soda by treatment with lime.

The tar acids, which still contain some residue and some Water are distilled to obtain three portions, residue, dry tar acids and a mixture of tar acids and water. The residue is discarded, and the tar acid and water mixture permitted to settle. Upon settling a quantity of water is recovered which may be discarded or added back to the phenolate solution being recycled. There remains crude tar acids which together with the tar acids recovered directly from the distillation, may be treated in any suitable manner to further refine them or to separate them into the individual tar acids.

While the process and system of apparatus described above are the preferred form, it is to be understood that considerable modifications may be made in both the process and the apparatus without departing from the principles of this invention. For example, any suitable device may be substituted for the constant head pumps and the proportioning meter, for feeding accurately-proportioned amountsrof caustic soda solution, tar and phenolate solution or water to the mixer, The phenolate solution or Water may be added at any time during the mixing and the constituents may be heated either before or after mixing to a temperature of around 80 C., or the process may be performed without the application of heat to the constituents prior to the centrifuging. Also, although it is definitely preferred to use a centrifuge to separate the phenolate solution from the tar, other means of separation, such as gravity or filtration may conceivably be employed.

As has already been indicated, the phenolate solution resulting from the treat-ment is recycled either in whole or in part and this recycling may be carried out to any desired extent, thus building up a concentration of phenolates in the solution of anywhere from 5 to 40% or even greater. Preferably, in order to make the process economical, the concentration is built up to at least or 20% and may be much higher. 1f the process is to be performed by the batch, all ofthe phenolate solution or at least a major part of it will ordinarily be drawn off at one time, whereas if the process is to be performed continuously a smaller portion, usually from 5 to 15%, by volume will be removed to the recovery apparatus continuously.

In the recovery of the tar acids from the phenolate solution the steps and the apparatus may also be modied. Thus, the phenolate solution may be passed to the springing tower without previous heating or the phenolate solution may be treated with sulphuric acid instead of stack gas to liberate the tar acids. If desired, the tar acids may be taken directly from the rst settling tank without any further distillation and used in this condition or passed to other apparatus for puriiication.

I claim:

l. A process of removing tar acids from tar that comprises separately mixing with the tar a constant proportion of an aqueous caustic soda solution and a constant proportion of water, centrifuging the resulting mixture to remove the tar, recycling the aqueous liquid recovered from the centrifuge by mixing it with additional tar and recovering the tar acids from the recycled aqueous liquid.

2. A process of removing tar acids from tar that comprises separately mixing with the tar a constant proportion of an aqueous caustic soda solution and a constant proportion of water, centrifuging the resulting mixture to remove the tar, recycling the aqueous liquid recovered from the centrifuge by mixing it with additional tar and additional caustic soda solution, and recovering the tar acids from the recycled aqueous liquid.

3. A process of removing tar acids from tar that comprises mixing with the tar a constant proportion of caustic soda and a constant proportion of Water, centrifuging the resulting mixture to remove the tar, recycling the aqueous liquid recovered from the centrifuge a plurality of times by mixing it with additional tar and recovering the tar acids from the recycled aqueous liquid.

4. A process of removing tar acids from tar that comprises separately mixing with the tar a constant proportion of an aqueous caustic soda solution and a constant proportion of water, heating the mixture to around C., centrifuging the resulting mixture to remove the tar, recycling the aqueous liquid recovered from the centrifuge a plurality of times by mixing it with additional tar and additional caustic soda solution, and recovering the tar acids from the recycled aqueous liquid.

5. A continuous process for the removal of tar acids from tar that comprises continuously and separately mixing with tar an aqueous caustic soda solution and water in predetermined proportions, heating the mixture to around 80 C., continuously centrifuging to separate the mixture so formed into a tarry and an aqueous phase,

' continuously returning a portion of the aqueous phase to the process to be mixed with the tar; and continuously withdrawing a portion of the aqueous phase and recovering tar acids therefrom.

6. A process for the recovery of tar acids from tar that comprises mixing with tar an aqueous caustic soda solution containing about 8% caustic soda by weight and in such proportion that approximately 1.4 pounds of caustic soda are added for each gallon of tar acids in the tar, mixing with these two constituents water in the proportion of approximately two gallons of the aqueous liquid to each gallon of tar, heating the mixture to approximately 80 C., centrifuging to resolve the mixture into a tarry portion and an aqueous portion, recycling the aqueous portion as at least a part of the aqueous liquid added to the tar and caustic soda solution, and thereafter passing the said aqueous portion into contact with a gas containing carbon dioxide whereby the tar acids are precipitated therefrom, settling to separate the tar acids from the aqueous solution and distilling the tar acids so separated.

'7. A continuous process for the removal of tar acids from crude undistilled tar having a speciiic gravity in excess of 1.06 that comprises continuously mixing the crude tar with an aqueous alkaline solutionv to convert the tar acid content of said crude tar into the corresponding salts of said tar acids, passing the mixture of crude tar and the aqueous solution of said salts formed by a reaction of the alkaline solution with said tar acids continuously through a centrifugal separator and thereby separating the mixture into a tarry and an aqueous phase, continuously returning a portion of the aqueous phase separated from the centrifugal separator into confluence with alkali and a further quantity of said crude tar and continuously withdrawing a portion of the aqueous phase and recovering tar acids therefrom.

8. A process for the removal of tar acids from crude undistilled tar having a specic gravity in excess of 1.06 that comprises mixing the crude tar with an aqueous alkaline solution to convert the tar acid content of said crude tar into the corresponding salts of said tar acids, passing the mixture of crude tar and the aqueous solution of said salts formed by a reaction of the alkaline solution with said tar acids through a centrifugal separator and thereby separating the mixture into a tarry and an aqueous phase, returning a portion of the aqueous phase separated from the centrifugal separator into confluence with alkali and a further quantity of said crude tar and withdrawing a portion of the aqueous phase and recovering tar acids therefrom.

JULIUS GEORGE HATMAN.

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